The use of metallurgically bonded, dissimilar sheet metal has been known to the art of hermetic connector manufacturing for a number of years. One method used to manufacture this bonded sheet metal is through the use of explosives in a process called explosive welding. An explosive weld connotes the metallurgical bond created at the point of impact when one metal sheet is driven into another by the force of an explosion. An explosive weld is distinguished, for example, from a friction weld, i.e. the metallurgical bond created between two metals when they are rubbed together under high pressure conditions. A dissimilar metals sheet is a sheet of metal consisting of two or more layers of distinctly different metals which have been joined together by, for example, explosive welding. Other ways to produce dissimilar metal sheet material exist, for example friction welding, roll bonding and supersonic forming.
Similar metals may be interfaced with each other by standard procedures such as brazing, soldering, laser welding or the like. Dissimilar metals, e.g., metals characterized by differing thermal expansion properties, melting points, weld incompatibility or the like, do not reliably interface using such standard procedures. For example, iron cannot be reliably laser welded to aluminum and solder joints between iron and aluminum have a definite thermal fatigue cycle life due to the significant difference in their thermal expansion properties. As a result, iron-based metal connectors cannot be reliably soldered or laser welded to aluminum electronics packages for sustained periods of operation.
The introduction of the transition bushing, i.e., a ring cut from a sheet of dissimilar metal that consists of at least two different metals with the purpose of providing one metal to interface with a connector and the other to interface with an electronics package, has provided a solution to the problems associated with the standard connector mounting process, such as the inability to weld dissimilar metals or the unreliable process of soldering incompatible metals together. For example, the transition bushings described in the U.S. patent to Sharp et al, U.S. Pat. No. 5,109,594 and the U.S. patent to Rapoza, U.S. Pat. No. 5,110,307 allow low expansion iron-based connectors to be interfaced to a high expansion electronic package, such as aluminum.
Transition bushings have a number of drawbacks, some of which are detailed in the U.S. patent to Taylor, U.S. Pat. No. 5,298,683; these include the increased size and weight of the connector assembly when a transition bushing is added, as well as the addition of another component to the assembly parts list. The transition bushing can be incorporated into the connector shell if a custom connector is designed with this approach in mind, as detailed in the above-referenced patent to Taylor and the U.S. patent to Snow, U.S. Pat. No. 4,690,480. The integration of the dissimilar metal sheet material into the connector body is one way to decrease the size and weight of the connector assembly. It also addresses the drawback of an extra component because the transition bushing, rather than being a separate part, is now part of the connector.
All prior art connectors designed per the Snow, Sharp, Rapoza or Taylor patents are manufactured from two main components. The first component is the exterior portion of the connector, which is always manufactured from dissimilar metals sheet material. This part of the connector can be in the form of a transition bushing or a dissimilar metal sheet can be used to provide a connector shell, also known as the connector body.
The second main component is the part of the connector that contains the hermetically sealed, electrically insulated feed through pin. This part can take the form of a standard one piece connector when used in conjunction with a transition bushing as described in the Rapoza patent or a multi-pin header as described in the Sharp patent. It can also take the form of a simple single pin feed through as described in the Snow and Taylor patents, as well as a multi-pin insert assembly as further described in the Taylor patent.
A common feature of all the prior art connectors is the fact that the dissimilar metal component is never part of the dielectric sealing process. The dielectric material, usually glass or ceramic, surrounds the feed through pin and is sealed into the second main component through a high temperature process of brazing or glass/ceramic fusion, i.e., melting the glass or ceramic dielectric material, allowing it to flow into the cavity of the second component around the feed through pin.
This type of connector architecture is diagrammatically illustrated in the side sectional view of FIG. 1. As shown therein, a first main component of the connector comprises an outer connector shell or body 10, which is typically made of dissimilar metal sheet material composed of aluminum and stainless steel, and a second main component comprising an interior insert 20 made of stainless steel. The connector shell 10 is configured so as to surround and abut against the outer extremity of the stainless steel insert 20. The latter is provided with a plurality of parallel holes or apertures 22 that are sized to receive associated connector pins 24. These connector pins are held in place and hermetically sealed within the apertures 22 by means of a glass or ceramic material 26, which fill those portions of the apertures surrounding the individual pins 24. Also shown in Figure is a perforated interfacial gasket 28, through apertures in which upper portions 25 of the pins 24 protrude, as shown. Lower portions 27 of the pins extend outwardly from the bottom of the stainless steel insert, as shown.
In this-type of connector architecture, the stainless steel insert 20 is secured to the surrounding shell 10 by means of a laser weld joint 30 formed between the bottom peripheral edge 21 of the insert 20 and the bottom peripheral edge 31 of an adjacent stainless steel piece 32, shown in cross-section as having a generally inverted ‘L’ shape. This inverted L shaped stainless steel piece 32 is a typical example of the small amount of stainless steel which is left as part of the connector shell after machining the shell from the explosion welded dissimilar metal material. It is typically bonded to a bottom region 12 of the surrounding shell 10 by explosion bonding, so as to form a generally annular ribbon-configured explosion bond region around the underside of the shell 10 to which the insert 20 may be laser welded. The shell is further shown as having a pair of threaded jack posts 14 and 15, and may be welded or soldered to an adjacent housing 40. A drawback to the structure shown in FIG. 1 is the relative narrowness of the annular shaped explosion bond formed between the inverted L-shaped stainless steel piece 32 and the underside of the connector shell 10, which facilitates the propagation of defects in the explosion bond region.